Our data indicate that terminally differentiated chicken myotubes can be infected with Rous Sarcoma Virus (RSV) and the virus replicates in myotubes without expression of the src gene (the gene responsible for oncogenic transformation) in the complete absence of host DNA synthesis. Myotubes are permanently withdrawn from the cell cycle and no DNA synthesis takes place. We shall examine by DNA restriction endonuclease analysis, the nature of unintegrated viral DNA as well as the possible integration of viral DNA at a specific site of myotube DNA. Infection of myotubes with RSV did not induce host DNA synthesis or other expression of functional src gene product. The reasons for the observed absence of the src gene expression during RSV production will be explored. The processing of viral RNA will be examined by subjecting the total RNA from infected myotubes to sucrose gradient centrifugation or gel electrophoresis, followed by hybridization with viral 32P complementary DNA. The possibility that a non-functional but immunologically cross-reacting src protein may be present in infected myotubes will be examined by following incorporation of 35S methionine into the protein precipated by the anti-src antibody. The non-functional src product, if detected, will be characterized as to its possible protein kinase activity, molecular weight, and primary aminoacid sequence. Attachment and budding of RSV in infected myotubes will be examined by electron microscopy.